Separable connectors are universally employed for electrical connections in residential and commercial buildings. Typically a standard male plug from an electrical product is inserted into the female socket. The contacts in the socket largely determine the force required to extract the plug.
Contacts with inadequate pressure can let the male plug work away from the face of the socket thereby allowing small objects to fall onto the prongs of the male plug. Light pulling forces on the cord may result in partial extraction and the user can accidentally touch the prongs and experience electric shock. Ultimately, an inadvertent pulling force may completely release the plug and terminate power to the electrical product.
Sockets with contacts that tightly retain a power plug can hurt people. Tight power cords connected to multiple items of portable electronic equipment in hospital rooms frequently cause tripping injuries to patients and staff. There is associated damage when equipment is pulled off a shelf or otherwise upset. Occasionally instruments are dragged from a mobile cart by inadvertent movement. The problem is amplified in operating rooms where managing the number of power cords is increasingly difficult. Intravenous pumps, monitors and the like used during lengthy surgery add multiple connections to facility power. There are corresponding difficulties in homes and businesses, including appliances where follow through from a hard pull can drive a person's hand into a nearby object, or when a tight plug has to be tediously worked back and forth to disengage it from the receptacle. Furthermore, operators frequently pull on the power cord to disconnect a plug that is out of reach, obscured or otherwise difficult to remove. Such a pull against tight contacts incurs a high risk of breaking the wire inside the cord.
Considerations in design of a contact to reduce the risks discussed above include ensuring that the optimum contact pressures established in manufacture are maintained during the life of the contact, and that the optimum release pressures are maintained for plug extraction when pulls on the cord are at angles substantially away from normal to the face of the socket.
Double wipes are a type of contact predominately found in conventional wiring devices such as wall receptacles, socket adapters, power strips, extension cords and the like which typically do not maintain a constant release force over time. Numerous conventional double wipe contact clips have their opposing blades interconnected in various ways such as riveting, staking and welding. A rivet or weld tends to deform or creep over a period of time, resulting in subsequent failure of the contact members to maintain proper contact pressure. Also, the conventional devices often do not adequately prevent separation between the contact blades when the male prong is inserted, leading to stresses that exceed the yield point of the material forming the contact. Increasing blade length helps in decreasing the bending stresses but usually it is not possible to increase the blade lengths because there are various constraints imposed on maximum blade length in conventional devices.
Many connectors are known which provide a high contact pressure and a light extraction force by utilizing a manually releasable self-locking mechanism. A manually actuated easy release however, is not effective when immediate plug separation is needed to prevent injury or damage. An operator is not likely to be near the receptacle, nor would he have time to take the release action.
Known receptacles typically suffer from other disadvantages related to safety risks:
(1) A plug may only be partially inserted by a careless operator, (2) a plug can work its way out when subjected to inadvertent pulls less than required to extract the plug, (3) vibration at the receptacle can loosen a plug, and (4) the male plug may only be extracted with a pulling force substantially normal to the face of the socket.